Vehicle, transportation and marine glazing systems for many years have sought to reduce solar heat load through the glazing while maintaining a desired level of visible transmission. The primary drivers for this are occupant comfort, reduced air conditioning load, improved fuel economy and reduced emissions.
Solutions often employ tinted glass to reduce visible light transmission and mitigate solar heat gain in vehicle cabins. Such solutions are often referred to as absorbing solutions as they absorb a portion of the solar spectrum, with this energy being converted into direct heating of the glass/window assembly. Absorbing glass solutions are used in both laminated and monolithic applications, with all glass substrates being tinted in laminated applications. Such solutions have the advantages of reducing direct solar transmitted energy while improving comfort. However, a primary disadvantage of absorbing solutions is that the heat gained by the assembly is subsequently rejected or re-radiated in all directions, and therefore a portion of the heat is transferred to the interior space of the vehicle or the like thereby becoming a secondary source of undesired heat. This effect of secondary heat is recognized and quantified by many standards of calculation of solar load through glazing such as NFRC solar heat gain coefficient (SHGC), or Tts (Total Solar Transmission) per ISO 13837. SF (G-Factor; EN410-673 2011) and SHGC (NFRC-2001) values are calculated from the full spectrum and may be measured with a spectrophotometer such as a Perkin Elmer 1050. In each case, these values represent the sum of the direct solar transmission and secondary re-radiated heat components. For example, most tinted/absorbing glass solutions having a visible transmission (Tvis) over 70% typically exhibit a Tts or SHGC in the range of 53-65%, compared with clear glass having a Tts or SHGC of about 80%. In the case of lower Tvis absorbing solutions the Tts can be lower. For example, a Tvis in the range of 15-20% can yield a Tts or SHGC around 40%.
Silver based low-E coatings have also been used in vehicle windshields to improve solar heat rejection. Such silver based low-E coatings are typically provided between the glass substrates of a laminated windshield. The advantage of silver based low-E coatings is the fact that a significant portion of the solar energy is reflected by the window, rather than absorbed, hence mitigating a large portion of secondary heating. Thus, such reflecting solutions typically have about 8-15% lower Tts than a comparable Tvis absorbing solution. The disadvantage of these silver based low-E reflecting solutions is primarily related to their cost and complexity of manufacture at the fabrication level. Silver based low-E coatings are typically soft and easily damaged in processing as well as being susceptible to damage from the heating processes use to strengthen or shape the glass. In addition, such reflective solutions also tend to significantly increase visible reflection from one or both sides of the window creating additional potential interior glare and undesirable outward color effects. The exterior appearance of such solutions is often very notably different from that of regular glazings and in most cases is perceived negatively.
In certain example embodiments of this invention, it has been found that applying a low-E coating having a TCO such as ITO, which is surface durable, to the inside surface of a solar absorbing assembly provides for an improvement in the solar heat gain of the assembly. An ITO based coating with an emissivity of around 0.17-0.22 for example can result in a reduction of SHGC or Tts of at least about 0.05 (5%), more preferably of at least about 0.10 (10%), absolute, compared to if no such coating is provided. Further, in the case of a laminate window, it has been surprisingly found that using a hybrid including an absorbing tinted glass (e.g., relatively high iron glass) for the outboard glass substrate and a different low absorption clear glass (e.g., relatively low iron glass) for the inboard glass substrate, with the ITO-based low-E coating on the surface of the inboard glass substrate to face the vehicle interior, is advantageous in that solar heat gain performance can be further improved compared to when the same glass is used for both substrates along with the same coating.
Thus, certain example embodiments of this invention relate to a laminated window (e.g., vehicle window, marine vehicle, or building window) having different glass substrates and an ITO-based low-emissivity (low-E) coating on an interior surface thereof, so that the ITO-based low-E coating is to be located adjacent and exposed to the vehicle interior or building interior. In certain example embodiments, exterior/outboard and interior/inboard glass substrates of the window are laminated to each other via a laminating material such as polyvinyl butyral (PVB), ethylene-vinyl acetate (EVA), or the like. No low-E coating is provided between the glass substrates in certain example embodiments. Instead, the low-E coating, including a transparent conductive oxide (TCO) layer of a material such as indium-tin-oxide (ITO), is provide on the surface of the interior glass substrate so as to face and be exposed to the vehicle interior or building interior. In certain example embodiments of this invention, the exterior glass substrate contains more iron, and is thus more absorbing of IR radiation, than the interior glass substrate. It has surprisingly been found that this hybrid approach including an absorbing relatively high iron glass substrate on the outboard side, and a clear relatively low iron glass substrate on the inboard side, with the low-E coating on the clear inboard glass substrate facing the vehicle interior or building interior, results in a laminated window having improved solar heat gain performance compared to using the same glass for both the inboard and outboard glass substrates. In certain example embodiments, the low-E coating may be of or include a TCO layer such as ITO located between first and second dielectric layers which may be of or include silicon oxynitride, silicon nitride, and/or the like. The coating is sufficiently durable to survive in exposed environments, and also has a sufficiently low hemispherical emissivity such that the window can retain heat from the vehicle/building interior, thereby improving solar heat gain characteristics and/or reducing the likelihood of condensation thereon.
In certain example embodiments, the ITO-based coating on at least one glass substrate is heat treated (e.g., at a temperature of at least 580 degrees C. for at least about 2 minutes, more preferably at least about 5 minutes), and may be thermally tempered and/or heat bent in this respect. The heat treatment, for example, may be used to activate the ITO-based coating and reduce its sheet resistance and emittance, and/or may be used for thermal tempering and/or heat bending of the glass of the window. In certain example embodiments of this invention, following such heat treatment (HT), the ITO-based coating may have a hemispherical emissivity of no greater than 0.40 (more preferably no greater than 0.30, and most preferably no greater than 0.25) and/or a sheet resistance (Rs) of no greater than 30 ohms/square (more preferably no greater than 25 ohms/square, and most preferably no greater than 20 ohms/square).
In an example embodiment of this invention, there is provided a vehicle (e.g., car, truck, train, bus, or boat) window comprising: first and second glass substrates laminated to each other via a polymer inclusive interlayer, wherein the first glass substrate is configured to be located closer to a vehicle interior than is the second glass substrate; a multi-layer coating on the first glass substrate and configured to be located adjacent and exposed to a vehicle interior, so that the coating is not located between the first and second glass substrates, wherein the coating has a sheet resistance (Rs) of no greater than 32 ohms/square and comprises a transparent conductive layer comprising indium-tin-oxide (ITO) located between and directly contacting first and second transparent dielectric layers, and wherein the first transparent dielectric layer is located between at least the first glass substrate and the transparent conductive layer comprising ITO; wherein a base glass composition of each of the first and second glass substrates comprises (wt. %) SiO2 67-75%, Na2O 10-20%, CaO 5-15%, MgO 0-5%, Al2O3 0-5%, K2O 0-5%; wherein the second glass substrate contains at least 0.25% more total iron (expressed as Fe2O3) than does the first glass substrate.
In another example embodiment of this invention, there is provided a window comprising: first and second glass substrates laminated to each other via a polymer inclusive interlayer, wherein the first glass substrate is configured to be located closer to a vehicle interior or building interior than is the second glass substrate; a multi-layer coating on the first glass substrate and configured to be located adjacent and exposed to a vehicle interior or building interior, so that the coating is not located between the first and second glass substrates, wherein the coating comprises a transparent conductive layer comprising indium-tin-oxide (ITO) located between and directly contacting first and second transparent dielectric layers, and wherein the first transparent dielectric layer is located between at least the first glass substrate and the transparent conductive layer comprising ITO; wherein a base glass composition of each of the first and second glass substrates comprises:
IngredientWt. %SiO267-75%Na2O10-20%CaO 5-15%MgO0-5%Al2O30-5%K2O 0-5%;wherein no low-E coating is provided between the first and second glass substrates; wherein the first and second dielectric layers are silicon based and comprise at least one of oxygen and nitrogen; wherein the coating comprises, moving away from the first glass substrate: the first dielectric layer, the first dielectric layer having an index of refraction of 1.60-1.90 and a thickness of from 10-120 nm, the layer comprising ITO, the layer comprising ITO having a thickness of from 75-175 nm, and the second dielectric layer, the second dielectric layer having an index of refraction of 1.60-1.90 and a thickness of from 10-120 nm; wherein the coating has a sheet resistance (Rs) of no greater than 25 ohms/square and a hemispherical emissivity of no greater than 0.30; and wherein the window has an SHGC value of no greater than 0.48.